How dangerous can a PDF that is downloaded from an email or off a website on the Internet be to my Mac. I recently watched a security presentation on YouTube, and the speaker made it sound like PDFs are one of your biggest threats. I am not a Bit Torrent type of person, but I do surf as much as the next person, and being a geek, I tend to download PDFs a lot when I am reading up on IT things. For instance, last night I found some "free" eBooks on a website and so I downloaded one not even thinking that it could be a risk. The eBook looks legitimate, but maybe it was infected with a root kit and know the Chinese have me in their sites?